Odd QOTD: How does a PC turn on?

[Conan257]

Need to know for another project, and don't want to wait till I get home with a multimeter before I get the answer...

Basically, i'm after a detailed description of the process by which pressing the button turns on a PC.

How does the 5v standby tie in?
What voltage does the green wire operate at?
Is the PC switch a momentary switch on turn on?

 

[JonSmith]

When you push the button it shorts the power button pins on the motherboard. When released the motherboard detects this and then indicates the PSU to turn on.

Essentially you want something that can short and then unshort the power button pins on the motherboard. The motherboard monitors the switches constantly, this is how you can set it so that pressing the power button makes the PC enter sleep mode or holding it for 4 seconds shuts down the computer.

The 5V standby just supplies 5V at up to 1A provided the PSU is plugged in, otherwise the motherboard wouldn't have power to detect the status of the switches.